Fluid dynamic bearing apparatus and a motor using the same

ABSTRACT

Assembly precision in a motor is improved and greater cost reduction is achieved. 
     A fluid dynamic bearing apparatus  1  comprising a housing  7  and bearing sleeve  8  as fixed-side members  2 , a shaft member  9  as a rotational-side member  3  having a portion  3   c  for mounting a rotor magnet  5 , and a disk hub  10 , the shaft member  9  being supported by the bearing sleeve  8  in the radial direction in a non-contact manner by the hydrodynamic effect of a lubricating oil produced in a radial bearing gap between the inner circumferential surface  8   a  of the bearing sleeve  8  and the outer circumferential surface  9   a  of the shaft member while the shaft member  9  is in rotation, the apparatus  1  comprising a disk hub  10  which is fixed on the shaft member  9  and has a portion  3   c  for mounting the rotor magnet  5 , and the disk hub  10  being a molded resin article formed by insert-molding using the shaft member  9  as an insert piece.

This application is a divisional of application Ser. No. 11/587,535,filed Jul. 12, 2007, now U.S. Pat. No. 7,819,585 which is the NationalStage of International Application No. PCT/JP2005/008891, filed May 16,2005.

FIELD OF THE INVENTION

The present invention relates to a fluid dynamic bearing apparatus whichsupports a shaft member by the hydrodynamic effect of a fluid which isproduced in a radial bearing gap in a non-contact manner.

This fluid dynamic bearing apparatus is for use in spindle motors fordisk apparatuses, polygon scanner motors for laser beam printers (LBP)and in other small motors. Enhanced speed, cost reduction, noisereduction, etc., as well as high rotational accuracy, are required forthese motors. One of the components which determine these requiredperformances is a bearing which supports the spindles of said motors. Inrecent years, the use of fluid dynamic bearings having excellentcharacteristics in terms of the required performances mentioned abovehas been studied or actually started.

For example, for a spindle motor of a disk drive unit such as HDD, afluid dynamic bearing apparatus which comprises a radial bearing portionwhich supports a shaft member in the radial direction in a non-contactmanner and a thrust bearing portion which supports the shaft member inthe thrust direction in a non-contact manner is used. At this time,hydrodynamic grooves are provided as a hydrodynamic pressure producingmeans on the inner circumferential surface of a bearing sleeve whichforms the radial bearing portion or on the outer circumferential surfaceof the shaft member. Moreover, the hydrodynamic grooves are alsoprovided on both end faces of a flange portion of the shaft member whichforms the thrust bearing portion or on the faces opposing these (endfaces of the bearing sleeve, end faces of a thrust plate fixed on ahousing, etc.) (for example, refer to Japanese Unexamined PatentPublication No. 2000-291648).

SUMMARY OF THE INVENTION

The spindle motor mentioned above is constituted of such a fluid dynamicbearing apparatus and many other parts such as a stator coil, rotormagnet and disk hub. To ensure high rotational performance required forthe increasingly high performance of information appliances, efforts toimprove the processing precision and assembly precision of each parthave been made. Meanwhile, a demand for cost reduction in this type ofmotors is increasing.

Therefore, an object of the present invention is to improve assemblyprecision in a motor, as well as to achieve further cost reduction.

To solve the object mentioned above, a fluid dynamic bearing apparatusaccording to the present invention comprises a fixed-side member and arotational-side member, supports the rotational-side member by thehydrodynamic effect of a fluid which is produced in an annular radialbearing gap between the fixed-side member and the rotational-side memberin the radial direction in a non-contact manner, the rotational-sidemember having a portion for mounting a rotor magnet and being aninjection-molded article of a resin using a metal part as an insertpiece. The rotational-side member herein comprises at least a memberhaving a portion for mounting a rotor magnet and a metal part. Theportion for mounting a rotor magnet may be composed of the metal part.The metal part may have any shape or function, and comprises parts whichare essential for its bearing function, or parts added to improve itsbearing function. Examples of the “member having a portion for mountinga rotor magnet” include disk hubs and turntables for supporting magneticdisks and like disks and rotor components for attaching polygon mirrors,among others.

Forming the rotational-side member of a resin material enables a greaterreduction in weight than forming a metal by machining or like means, andit also allows production at a low cost. In particular, reduction in theweight of the rotational-side member allows rapid start and stop of themotor. Moreover, by injection-molding the rotational-side member using ametal part as an insert piece, the trouble of additionally mounting thedisk hub or like member and the metal part in a later process step canbe saved. The cost of assembling the motor can be thus reduced.Furthermore, the mounting precision between the disk hub or like membersand metal part can be improved, and sufficient fixing force can be alsoensured between them. Generally, the inaccuracies of the rotational-sidemember can greatly affect the bearing performance, for example, it canbe a cause for shaft runout or other problems. According to the presentinvention, lowered bearing performance resulting from inaccuracies inmounting can be avoided.

Examples of metal parts which are insert-molded integrally with therotational-side member include the shaft member facing the radialbearing gap. According to this, the disk hub, turntable, rotor memberand like parts which are originally components of the motor which areoriginally components of the motor can be integrated into the fluiddynamic bearing apparatus together with the shaft member to form anassembly as a component of the fluid dynamic bearing apparatus.Therefore, in the assembly step of the motor, the operation of mountingof these components on the shaft member can be dispensed with, and thecost of assembling the motor can be reduced. The shaft member as a metalpart is not necessarily entirely formed of a metal. For example, thehollow portion of a cylindrical metallic material can be filled with aresin during insert molding, whereby the shaft member can be a compositearticle of a metal and a resin.

Moreover, another example of metal parts which is insert-moldedintegrally with the rotational-side member is a core.

As mentioned above, when the rotational-side member is molded of a resinmaterial, the greater the thickness of the member, the greater theamount of the shrinkage and the dimensional change caused by a change intemperature during use. Since in the present invention, therotational-side member is injection-molded of a resin material with acore made of metal as an insert piece and part of the resin portion isreplaced by the core, reduction in the weight of the rotational-sidemember and in the production cost can be achieved, and at the same thedimensional change during molding and during use can be reduced toincrease the dimensional accuracy of the rotational-side member. Thecore can be installed throughout the entire rotational-side member, orit can be partially installed only in a region where the amount of thedimensional change of the resin is large. From a perspective ofminimizing the amount of dimensional change, it is desirable that thecore is embedded in the rotational-side member. However, part of it maybe exposed over the rotational-side member if it causes no problem.

The core can be formed of, for example, a magnetic substance. Accordingto this, the leakage of magnetic flux produced between the stator coiland rotor magnet through the rotational-side member can be prevented.

The core can also be formed of, for example, a porous body such as asintered metal. According to this, the anchor effect produced in thesurface opening of the porous body makes the resin portion covering thecore to grip well on the core and resin portion and increases thesticking strength of the core.

Moreover, to solve the object mentioned above, the fluid dynamic bearingapparatus according to the present invention comprises a shaft member, afixed-side member which freely rotatably supports the shaft member, amember which is attached to the shaft member and has a portion formounting a rotor magnet, the shaft member being supported in the radialdirection in a non-contact manner by the hydrodynamic effect of a fluidwhich is produced in an annular radial bearing gap between thefixed-side member and the shaft member, the member having a portion formounting a rotor magnet being molded of a resin, and in this memberhaving a portion for mounting a rotor magnet, a magnetic shieldingmember comprising a magnetic substance being disposed at least in aportion which opposes the rotor magnet.

Molding the member having a portion for mounting a rotor magnet of aresin material enables weight reduction greater than in a componentmolded of metal by machining or other means and production at a lowcost. In particular, the reduction of the weight of the member having aportion for mounting a rotor magnet allows rapid start and stop of themotor. When the member having a portion for mounting a rotor magnet ismade of a resin as stated above, the magnetic flux produced between thestator coil and rotor magnet may leak through the member having themounting portion to cause magnetic force loss. In the member having aportion for mounting a rotor magnet, however, a magnetic shieldingmember comprising the magnetic substance at least in the portionopposing the rotor magnet can be disposed to prevent such leakage ofmagnetic flux and improve the rotational performance of the motor.

By making the member having a portion for mounting a rotor magnet aninjection-molded article of a resin using the magnetic shielding memberas an insert piece, the trouble of additionally mounting the disk huband like members and magnetic shielding member in later process stepscan be saved, and the cost of assembling the motor can be reduced. Themember having a portion for mounting a rotor magnet can be alsoinjection-molded of a resin material using the magnetic shielding memberand shaft member as insert pieces, whereby a further reduction inassembling cost can be achieved.

In insert molding, it is desirable that the magnetic shielding member isat least partially embedded in the resin portion of the member having aportion for mounting a rotor magnet. This causes the regions in theresin portion covering the embedded portion of the magnetic shieldingmember opposing each other to shrink in the direction that clamps themagnetic shielding member when cured. Therefore, the fixing forcebetween the resin portion and magnetic shielding member can be furtherincreased.

Various substances are usable as materials for the aforementionedmagnetic shielding member insofar as the substance exhibits a magneticproperty. For example, metallic materials including stainless steel andtheir oxides, ceramics and the like can be suitably used. Moreover, whenthe magnetic shielding member is formed of the above metal, thesemagnetic shielding members are desirably formed by, for example, pressworking or like plastic processing, whereby they can be formed moreeconomically than in the case where the magnetic shielding member isformed by cutting or like means.

The fluid dynamic bearing apparatus mentioned above can be provided witha thrust bearing portion which freely rotatably supports the shaftmember in the thrust direction. Various structures are possible for sucha thrust bearing portion. For example, when the fixed-side member has abearing sleeve with the shaft member inserted at its inner periphery anda housing comprising the bearing sleeve fixed thereinside and an openingportion on one end side and an integral or a separate bottom on theother end side, a structure in which a thrust bearing gap is provedbetween the opening portion of the housing and the rotational-sidemember (the member having a portion for mounting a rotor magnet) and theshaft member is supported in the thrust direction in a non-contactmanner by the hydrodynamic effect of a fluid produced in this thrustbearing gap can be considered (refer to FIGS. 2, 5, 6 and 7).

Another possible example of the thrust bearing portion is that in whicha thrust bearing gap is provided between the bottom of the housing andthe shaft member and the shaft member is supported in the thrustdirection in a non-contact manner by the hydrodynamic effect of a fluidproduced in this thrust bearing gap (refer to FIG. 8).

Still another possible thrust bearing portion is that in which the shaftmember is contactingly supported by housing. In this case, the shaftmember contacts the bottom of the housing or other members constitutingthe bottom of the housing (such as a thrust plate, etc.) (refer to FIG.9).

The fluid dynamic bearing apparatus which produces a series of theseeffects can be suitably provided as a motor constituted of this fluiddynamic bearing apparatus, a rotor magnet, a stator coil which producesexcitation between itself and the rotor magnet.

As mentioned above, according to the fluid dynamic bearing apparatus ofthe present invention, since the rotational-side member is a moldedresin article, the weight and cost of the rotational-side member can bereduced. Further, the rotational-side member is insert-molded togetherwith the metal parts so that molding and assembly of the rotational-sidemember can be carried out in one step. Accordingly, the production costof the motor can be reduced and at the same time molding precision andassembly precision of the rotational-side member can be increased.Moreover, by providing the magnetic shielding member, the leakage of themagnetic flux can be suppressed and the rotational performance of themotor can be increased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a spindle motor informationappliances integrating the fluid dynamic bearing apparatus according tothe first embodiment of the present invention.

FIG. 2 is across-sectional view of the fluid dynamic bearing apparatusaccording to the first embodiment.

FIG. 3 is a drawing of a housing seen from the direction A in FIG. 2.

FIG. 4 is a cross-sectional view of a bearing sleeve.

FIG. 5 is a cross-sectional view showing one variation example of thefluid dynamic bearing apparatus according to the first embodiment.

FIG. 6 is a cross-sectional view showing one variation example of thefluid dynamic bearing apparatus according to the first embodiment.

FIG. 7 is an enlarged sectional view of a spindle motor for informationappliances integrating a fluid dynamic bearing apparatus according to asecond embodiment of the present invention for information appliances.

FIG. 8 is an enlarged sectional view of a spindle motor for informationappliances integrating a fluid dynamic bearing apparatus according tothe third embodiment of the present invention.

FIG. 9 is an enlarged sectional view of a polygon scanner motorintegrating a fluid dynamic bearing apparatus according to the fourthembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described below withreference to drawings.

FIG. 1 shows a constitutional example of a spindle motor for informationappliances incorporating a fluid dynamic bearing apparatus 1 accordingto a first embodiment of the present invention. This spindle motor forinformation appliances is for use in disk drive units such as HDD, andcomprises a fluid dynamic bearing apparatus 1 having a fixed-side member2 and having a rotational-side member 3 which is freely rotatablerelative to the fixed-side member 2 and, for example, a stator coil 4and a rotor magnet 5 which oppose each other across a gap in the radialdirection, and a bracket 6. The stator coil 4 is attached on the innerside face 6 a of the bracket 6, and the rotor magnet 5 is attached onthe outer periphery of the rotational-side member 3, more specificallyon the outer periphery of a disk hub 10 which can retain one or aplurality of disk-shaped information recording media such as magneticdisks on its outer periphery. The housing 7 of the fluid dynamic bearingapparatus 1 is attached on the inner periphery of the bracket 6. Whenthe stator coil 4 is energized, the rotor magnet 5 is rotated by theexcitation produced between the stator coil 4 and rotor magnet 5, andaccordingly the rotational-side member 3 rotates.

The fluid dynamic bearing apparatus 1 comprises a fixed-side member 2and a rotational-side member 3. The fixed-side member 2 is, as shown inFIG. 2, for example, constituted mainly of the housing 7 and bearingsleeve 8, and the rotational-side member 3 is constituted mainly of ashaft member 9 and the disk hub 10.

The shaft member 9 is formed by, for example, cutting or forging ametallic material such as stainless steel, and is inserted at the innerperiphery of the bearing sleeve 8. In a state that this shaft member 9is inserted at the inner periphery of the bearing sleeve 8 and isrotated, between the inner circumferential surface 8 a of the bearingsleeve 8 and the outer circumferential surface 9 a of the shaft member9, a first radial bearing portion R1 and a second radial bearing portionR2 are formed separately in the axial direction. Moreover, a thrustbearing portion T1 is formed between an end face 7 a of an openingportion of the housing 7 and an end face 10 a 1 on the lower end face ofthe disk hub 10. It should be noted that for the sake of explanation,the side of the end face 7 a of an opening portion of the housing 7 isreferred to as the upper side, while the side opposite to the end face 7a of the opening portion is referred to as the lower side in thedescription below.

The housing 7 comprises a cylindrical side portion 7 b, a bottom 7 cwhich is positioned at the lower end of the side portion 7 b and isintegrated into or separated from the housing 7. The bottom 7 c in thisembodiment is formed integrally with the side portion 7 b, and, forexample, is injection-molded of a resin composition based on acrystalline resin such as liquid crystal polymers, PPS, PEEK and likeinto a bottomed cylindrical shape. On the end face 7 a of the openingportion which serves as a thrust bearing face of the thrust bearingportion T1, for example, as shown in FIG. 3, a plurality of hydrodynamicgrooves 7 a 1 having a spiral shape are formed. This hydrodynamic groove7 a 1 is formed when the housing is molded. That is, a groove patternfor forming the hydrodynamic grooves 7 a 1 is preliminarily processed ina portion for forming the end face 7 a of the opening portion, of a moldwhich forms the housing 7, and the shape of the above groove pattern istransferred onto the end face 7 a of an opening portion of the housing 7when the housing is molded, whereby the hydrodynamic grooves 7 a 1 canbe formed simultaneously with the molding of the housing 7. The housing7 comprises a tapering outer wall 7 d whose diameter gradually increasesto the top on the upper outer periphery of the side portion 7 b. Itshould be noted that in this embodiment, the bottom 7 c is, for example,formed integrally with the side portion 7 b by injection molding of theabove resin material, but the bottom 7 c may be formed separately fromthe side portion 7 b and attached to the side portion 7 b later. In thiscase, as shown in FIG. 6, for example, the lower end of the shaft member9 is provided with a flange portion 9 b, and a thrust bearing portion T2which supports the shaft member 9 in the thrust direction in anon-contact manner can be formed between the upper end face 9 b 1 of theflange portion 9 b and the lower end face 8 c of the bearing sleeve 8.

The bearing sleeve 8 can be formed, for example, of brass and likecopper alloys and aluminum alloy and like metals, or can be formed of aporous body comprising a sintered metal. In this embodiment, it isformed of a porous body of a sintered metal comprising copper as a mainingredient in a cylindrical shape, and is fixed in a predeterminedposition of the inner circumferential surface 7 e of the housing 7.

On the inner circumferential surface 8 a of the bearing sleeve 8, upperand lower regions which serve as radial bearing faces of the firstradial bearing portion R1 and second radial bearing portion R2 areprovided separately in the axial direction. In these two regions, asshown in FIG. 4, for example, a plurality of hydrodynamic grooves 8 a 1,8 a 2 are arranged each in a herringbone shape. The upper hydrodynamicgrooves 8 a 1 are formed axially asymmetrically relative to the axialcenter m (the axial center of the region between the upper and lowerslanted grooves), and the axial dimension X1 of the region above theaxial center m is greater than the axial dimension X2 of the regiontherebelow. Moreover, one or a plurality of axial grooves 8 b 1 areformed on the outer circumferential surface 8 b of the bearing sleeve 8throughout the axial length of the shaft. In this embodiment, threeaxial grooves 8 b 1 are formed at regular intervals in thecircumferential direction.

The disk hub 10 comprises an approximately disk-shaped base 10 a, aperipheral wall portion 10 b extending downwardly in the axial directionfrom the outer circumference 10 a 2 of the base 10 a, a brim 10 cprovided on the outer periphery of the peripheral wall portion 10 b anda disk loading face 10 d. A mounting portion 3 c for attaching the rotormagnet 5 in this embodiment is constituted of the outer circumferentialsurface 10 b 1 of the peripheral wall portion 10 b of the disk hub 10and a lower end face 10 c 1 of the brim 10 c. On the outercircumferential surface 10 b 1 and lower end face 10 c 1, the rotormagnet 5 is fixed, for example, by adhesion or like means so that therotor magnet 5 oppose the stator coil 4 (refer to FIG. 1) attached onthe inner side face 6 a of the bracket 6 in the radial direction.Moreover, the inner circumferential surface 10 b 2 of the peripheralwall portion 10 b forms an annular sealing space S whose dimension inthe radial direction gradually decreases from the side of the bottom 7 cof the housing 7 to the top between itself and the tapering outer wall 7d of the housing 7. This sealing space S is in communication with theouter diameter side of the thrust bearing gap of the thrust bearingportion T1 while the shaft member 9 and disk hub 10 are in rotation. Aslip-off prevention member 11 is fixed on the inner circumferentialsurface 10 b 2 of the peripheral wall portion 10 b. This slip-offprevention member 11 engages a shoulder 7 f formed on the outerperiphery of the housing 7 in the axial direction, whereby the shaftmember 9 and disk hub 10 are prevented from being pulled off upwardly.

The disk hub 10 of the above constitution is formed by injection-moldinga resin material using the shaft member 9 of a metal which is previouslyformed by cutting, forging process or the like as an insert piece. Bythis insert molding, the disk hub 10 and shaft member 9 are integratedin a state that the upper end of the shaft member 9 is embedded at thecenter of the base 10 a of the disk hub 10.

By forming the disk hub 10 integrally with the shaft member 9 by insertmolding in this manner, molding of the disk hub 10 and mounting processof the disk hub 10 to the shaft member 9 can be carried outsimultaneously. Therefore, the mounting process mentioned above can bedispensed with, and the assembly cost of the motor can be reduced.Moreover, when the disk hub 10 and shaft member 9 are integrally molded,using a high-precision mold to increase the positioning accuracy of theshaft member allows easily obtaining high mounting precision between thedisk hub 10 and shaft member 9. Furthermore, the runout precision orcoaxiality of the molded article can be maintained at a high level.Moreover, since the disk hub 10 is integrated in the shaft member 9 in astate that the shaft member 9 is partially embedded in the disk hub 10,a fixing force as high as or higher than in the case where it is fixedby adhesion, press fitting or like means can be obtained.

In addition to the shaft member 9, the rotor magnet 5 can be also usedas an insert piece for insert-molding the disk hub 10. This caneliminate a mounting process of the rotor magnet 5 to the disk hub 10and achieve greater cost reduction. Moreover, in this embodiment,hydrodynamic grooves 7 a 1 are formed on the end face 7 a of the openingportion of the housing 7. However, for example, a groove patterncorresponding to the hydrodynamic grooves 7 a 1 can be processed in aportion of the disk hub 10 corresponding to the thrust bearing face aforming mold to form hydrodynamic grooves on the disk hub 10simultaneously with the molding of the disk hub 10. In this case, sincethe hydrodynamic grooves of the thrust bearing face need not be formedseparately, a greater cost reduction is enabled.

The bearing sleeve 8 is fixed in a predetermined position of the innercircumferential surface 7 e of the housing 7 by, for example, adhesion(including loose adhesion, press fitting adhesion), press fitting,welding (including ultrasonic welding) or like fixing means. The shaftmember 9 is inserted at the inner periphery of the bearing sleeve 8fixed on the housing 7, and the disk hub 10 formed integrally with theshaft member 9 as stated above is integrated in the fixed-side member 2.The slip-off prevention member 11 is then fixed on the innercircumferential surface 10 b 2 of the peripheral wall portion 10 b ofthe disk hub 10 attached on the bearing sleeve 8 by press fitting,adhesion or like means.

In the fluid dynamic bearing apparatus 1 of the above constitution,while the shaft member 9 (rotational-side member 3) is in rotation, aregion which serves as the radial bearing faces of the innercircumferential surface 8 a of the bearing sleeve 8 (a region in whichupper and lower hydrodynamic grooves 8 a 1, 8 a 2 are formed) opposesthe outer circumferential surface 9 a of the shaft member 9 across theradial bearing gap. As the shaft member 9 rotates, the lubricating oilof the above radial bearing gap is pushed to the side of the axialcenter m of the hydrodynamic grooves 8 a 1, 8 a 2, and its pressure isincreased. The first radial bearing portion R1 and the second radialbearing portion R2 which support the shaft member 9 (rotational-sidemember 3) in the radial direction in a non-contact manner areconstituted by such hydrodynamic effect of the hydrodynamic grooves 8 a1, 8 a 2.

Similarly, in the thrust bearing gap between the end face 7 a of theopening portion of the housing 7 (region in which the hydrodynamicgrooves 7 a 1 are formed) and the end face 10 a 1 on the lower side ofthe opposing disk hub 10, an oil film of the lubricating oil is formedby the hydrodynamic effect of the hydrodynamic grooves. The first thrustbearing portion T1 which supports the shaft member 9 (rotational-sidemember 3) in the thrust direction in a non-contact manner is constitutedby this pressure of the oil film.

The first embodiment of the present invention is described above, butthe present invention is not limited to this embodiment. Anotherconstitutional example of the fluid dynamic bearing apparatus will bedescribed below. It should be noted that in the drawings shown below,parts and components having the same constitutions and functions as inthe first embodiment are referred to by the identical referencenumerals, and their repeated description will be omitted.

FIG. 5 shows a fluid dynamic bearing apparatus 1 according to avariation example of the first embodiment. A disk hub 13 in this fluiddynamic bearing apparatus 1 is, unlike in the first embodiment, a moldedresin article in which a core 12 made of a metal is further integratedtherein in addition to the shaft member 15. More specifically, the core12 has such a shape that a ring-shaped peripheral wall portion 12 bextends downwardly in the axial direction from the outer diameter sideedge 12 a 1 of an approximately disk-shaped base 12 a as well as thedisk hub 13, and has a thickness nearly constant throughout its entirebody. Both front and back faces of this core 12 and the tip of theperipheral wall portion 12 b are covered with a resin portion 14. Thedisk hub 13 is, for example, insert-molded by injection-molding a resinmaterial using the previously formed shaft member 15 and core 12 asinsert pieces. By this insert molding, the disk hub 13 and shaft member15 are integrated in a state that an upper end portion 15 a of the shaftmember 15 is embedded at the center of the base 12 a and the core 12 isembedded throughout the entire disk hub 13.

By forming the disk hub 13 having the core 12 embedded throughout theentire disk hub 13 in this manner from a resin material, the weight andproduction cost of the disk hub 13 can be reduced, and at the same timea dimensional change during molding and during use can be reduced andmolding dimensional accuracy of the disk hub 13 and thus of therotational-side member 3 can be increased. In the disk hub 13, it isdesirable that in a part where precision is particularly required, i.e.,the mounting portion of the rotor magnet 5 in the illustrated example,the thickness of the resin portion 14 is the same on both front and backsides of the core 12.

Moreover, in this embodiment, a shoulder 15 a 1 is formed in the upperend portion 15 a of the shaft member 15 embedded in the disk hub 13 ofthe shaft member 15, the core 12 exposed in the inner diameter portionof the disk hub 13 and the shaft member 15 are engaged in the axialdirection at the shoulder 15 a 1. Therefore, the positioning accuracy ofthe core 12 relative to the shaft member 15 can increased, and thereforethe mounting accuracy of the disk hub 13 to the shaft member 15 can beincreased.

The core 12 can be formed, for example, of a magnetic substance such asstainless steel. According to this, the magnetic flux which may passfrom the rotor magnet 5 to the inner diameter side via the disk hub 13is blocked by the core 12. Therefore, the magnetic flux produced betweenthe stator coil 4 and the rotor magnet 5 can be prevented from leaking.It should be noted that the core 12 can be die-formed, for example, bypress working and like plastic processing to enable production at alower cost.

In addition, the core 12 can be formed, for example, of a porous bodysuch as a sintered metal. According to this, since the resin portion 14around the core 12 is cured in a state that it bites into the pores onthe surface of the porous body, a kind of anchor effect is produced tothe core 12 and sticking strength between the resin portion 14 and thecore 12 is further increased.

FIG. 5 shows an example in which the core 12 and the shaft member 15 areboth insert pieces, but it is also possible that only the core 12 is aninsert piece for constituting the disk hub 13 by insert-molding. In thiscase, the shaft member 15 is fixed to the disk hub 13 which has beenmolded by a suitable means such as adhesion and press fitting.

FIG. 7 conceptionally and partially shows a constitutional example of afluid dynamic bearing apparatus 21 according to a second embodiment ofthe present invention and of a spindle motor for information appliancesintegrating this fluid dynamic bearing apparatus 21. This spindle motorfor information appliances is for use in disk drive units such as HDD,and comprises a fluid dynamic bearing apparatus 21 which freelyrotatably supports a shaft member 29 by a fixed-side member 2, a statorcoil 4 and a rotor magnet 5 which, for example, oppose each other acrossa gap in the radial direction (refer to FIG. 1) and a bracket 6. Therotor magnet 5 is attached on the outer periphery of a disk hub 30 as amember having a portion 3 c for mounting the rotor magnet 5. This diskhub 30 retains one or a plurality of magnetic disks and like disk-shapedinformation recording media on its outer periphery. The housing 7 of thefluid dynamic bearing apparatus 21 is attached on the inner periphery ofthe bracket 6. When the stator coil 4 is energized, the rotor magnet 5is rotated by the excitation produced between the stator coil 4 androtor magnet 5, and the housing 7 as a fixed-side member 2 and a diskhub 30, and thus a shaft member 29 rotate relative to a bearing sleeve 8accordingly.

The fluid dynamic bearing apparatus 21 in this drawing comprises thefixed-side member 2, the shaft member 29 which rotates relative to thefixed-side member 2, the disk hub 30 and a magnetic shielding member 28.In this embodiment, the parts on the rotation side (shaft member 29,disk hub 30, magnetic shielding member 28) will be mainly described.

The disk hub 30 as a member having the portion 3 c for mounting therotor magnet 5 is formed by injection-molding a resin composition basedon a liquid crystal polymers, PPS, PEEK or like crystalline resins, asmentioned above. The disk hub 30 of this embodiment comprises anapproximately disk-shaped base 30 a, a peripheral wall portion 30 bextending downwardly from the outer circumference 30 a 2 of the base 30a in the axial direction and a disk loading face 30 c provided on theouter periphery of the peripheral wall portion 30 b. The disk-shapedinformation recording media, which are not shown, are mounted on thedisk loading face 30 c, and are retained on the disk hub 30 by anappropriate retaining means, which is not shown. A magnetic shieldingmember 28 is attached to a lower end portion of the peripheral wallportion 30 b integrally with the disk hub 30.

The magnetic shielding member 28 is molded, for example, by plasticprocessing (press working, etc.) of a metal plate comprising aferromagnetic substance such as martensite-based stainless steel orferrite-based stainless steel. The magnetic shielding member 28 in thisembodiment has an approximately L shape in cross section, and comprisesan axial direction portion 28 a extending along the peripheral wallportion 30 b in the axial direction and a radial direction portion 28 bextending from the upper end of the axial direction portion 28 a to theouter diameter side. Of course, metallic materials other than stainlesssteel mentioned above, oxides of these metals, ceramics and othermaterials can be used for the magnetic shielding member as materials aslong as they are magnetic materials.

As mentioned above, the rotor magnet 5 is attached to the mountingportion 3 c of the disk hub 30 by adhesion or like means. In thisembodiment, the outer periphery (the outer periphery of the axialdirection portion 28 a) of the magnetic shielding member 28 provided inthe peripheral wall portion 30 b of the disk hub 30 is used as themounting portion 3 c and the rotor magnet 5 is fixed by adhesiondirectly to this mounting portion 3 c to realize metal adhesion andimprove the fixing force.

The disk hub 30 of the above constitution is molded by injection-moldinga resin material using the shaft member 29 which is previously moldedand magnetic shielding member 28 as insert pieces (insert molding). Bythis insert molding, the disk hub 30 and shaft member 29 are integratedin a state that the upper end of the shaft member 29 is embedded at thecenter of the base 30 a of the disk hub 30, and the disk hub 30 andmagnetic shielding member 28 are integrated in a state that the magneticshielding member 28 is embedded in the outer periphery of the peripheralwall portion 30 b of the disk hub 30. In the upper end portion of theshaft member 29, a groove 29 b is formed in the radial direction as aslip-off prevention for the disk hub 30 in the axial direction.

The disk hub 30 is molded integrally with the shaft member 29 andmagnetic shielding member 28 by insert molding in this manner, wherebythe molding of the disk hub 30 and the mounting processes of the diskhub 30, shaft member 29 and magnetic shielding member 28 can be carriedout simultaneously, and the assembling of the motor can be reduced.Moreover, in the insert molding, the positioning accuracy of the shaftmember 29 and magnetic shielding member 28 is increased by using ahigh-precision mold, thereby easily obtaining high mounting accuracy andmaintaining the runout precision and coaxiality of the molded article ata high level. The rotor magnet 5 can be further used as an insert piecein addition to the shaft member 29 and magnetic shielding member 28 forinjection-molding the disk hub 30.

Moreover, in the present invention the magnetic shielding member 28which functions as a magnetic shielding is disposed in a portion whichopposes the rotor magnet 5 in the disk hub 30. Leakage of the magneticflux which acts between the rotor magnet 5 and stator coil 4 via thedisk hub 30 can be prevented. Therefore, the magnetic flux densitybetween the rotor magnet 5 and the stator coil 4 opposing the rotormagnet 5 can be increased and the rotational performance of the can beimproved.

In order to prevent flux leakage, it is desirable that all the regionother than a portion of the rotor magnet 5 which opposes the stator coil4 is coated by the magnetic shielding member 28, but in this embodiment,considering the processability and other properties of the magneticshielding member 28, the magnetic shielding member 28 is provided withan axial direction portion 28 a and the radial direction portion 28 b toshield magnetism mainly at the inner diameter side and upper side of therotor magnet 5. Of course, the shape of the magnetic shielding member 28can be appropriately changed to shield the magnetism on another side(for example, lower side), or to limit the direction of the magneticshielding (for example, magnetism is shielded only at the inner diameterside).

Moreover in this embodiment, as shown in FIG. 7, the magnetic shieldingmember 28 and the disk hub 30 are molded integrally in a manner ofadhering the magnetic shielding member 28 to the outer periphery of thedisk hub 30 and the outer circumferential surface of the magneticshielding member 28 is exposed. However, part or the entire magneticshielding member 28 may be embedded in part of the disk hub 30. In thiscase, since a portion of the magnetic shielding member 28 which isembedded in the resin portion is bound by the shrinkage caused when amolten resin is cured from both sides, the sticking strength of themagnetic shielding member 28 can be increased.

In the fluid dynamic bearing apparatus 1 of the above-mentionedconstitution, while the shaft member 29 (disk hub 30) is in rotation,regions which serve as radial bearing faces of the inner circumferentialsurface 8 a of the bearing sleeve 8 (regions in which upper and lowerhydrodynamic grooves 8 a 1, 8 a 2 are formed) oppose the outercircumferential surface 29 a of the shaft member 29 across the radialbearing gap. As the shaft member 29 rotates, the lubricating oil in theabove radial bearing gap is pushed toward the side of the axial center mof the hydrodynamic grooves 8 a 1, 8 a 2 (refer to FIG. 4), and itspressure increases. By such hydrodynamic effect of the hydrodynamicgrooves 8 a 1, 8 a 2, a first radial bearing portion R1 and a secondradial bearing portion R2 which support the shaft member 29 (disk hub30) in the radial direction in a non-contact manner are constitutedrespectively.

Similarly, in the thrust bearing gap between the end face 7 a of theopening portion of the housing 7 (region in which the hydrodynamicgrooves 7 a 1 are formed) and an opposing lower end face 30 a 1 of thedisk hub 30, an oil film of the lubricating oil is formed by thehydrodynamic effect of the hydrodynamic grooves. By this pressure of theoil film, a first thrust bearing portion T1 which supports the shaftmember 29 (disk hub 30) in the thrust direction in a non-contact manneris constituted.

FIG. 7 (FIG. 1) shows a motor in which the stator coil 4 is disposed onthe inner diameter side and the rotor magnet 5 is disposed on the outerdiameter side as an example, but in contrast, the present invention canbe also applied to a motor in which the rotor magnet 5 is disposed onthe inner diameter side and the stator coil 4 is disposed on the outerdiameter side. Moreover, this Fig. shows a radial gap motor in which agap in the radial direction is provided between the stator coil 4 androtor magnet 5, but the present invention can be also applied to anaxial gap motor in which a gap is provided in the axial directionbetween the stator coil 4 and rotor magnet similarly.

FIG. 8 is an enlarged sectional view of a spindle motor for informationappliances integrating a fluid dynamic bearing apparatus 31 according toa third embodiment of the present invention. A thrust bearing gap isformed between the housing 7 and disk hub 10 (30) in the first andsecond embodiments, while in contrast, a thrust bearing gap is formedbetween the housing 37 and shaft member 39, and between the bearingsleeve 8 and shaft member 39, respectively, in this embodiment. Thisembodiment is different from the above-mentioned embodiments in thisterm. Specifically, the shaft member 39 comprises a flange portion 39 bprovided integrally or separately at its lower end. Moreover, a bottom37 b positioned in a lower end portion of the housing 37 is formedseparately from a side portion 37 a of the housing 37, and isretrofitted to the side portion 37 a. On the inner bottom face 37 b 1 ofthis bottom 37 b, although not illustrated, for example, hydrodynamicgrooves having the same shape as in FIG. 3 are formed, and hydrodynamicgrooves having a similar shape (having the opposite spiral direction)are formed on the lower end face 28 c of the bearing sleeve 8. In astate that the above shaft member 39 is inserted at the inner peripheryof the bearing sleeve 8 and rotated, a thrust bearing gap is formedbetween the lower end face 8 c of the bearing sleeve 8 and a upper endface 39 b 1 of the flange portion 39 b of the shaft member 39, andhydrodynamic effect of the lubricating oil is produced in this thrustbearing gap, thereby forming a first thrust bearing portion T11 whichsupports the shaft member 39 in the thrust direction in a non-contactmanner. Simultaneously, a thrust bearing gap is also formed between theinner bottom face 37 b 1 of the bottom 37 b attached to a lower endportion of the housing 37 and the lower end face 39 b 2 of the flangeportion 39 b. The hydrodynamic effect produced of the lubricating oil inthis thrust bearing gap forms a second thrust bearing portion T12 whichsupports the shaft member 39 in the thrust direction in a non-contactmanner.

In this embodiment, the disk hub 40 which retains magnetic disks andlike disks is insert-molded by injection molding a resin material usingthe shaft member 39 previously formed by forging or other means as aninsert piece, and, although not illustrated, the magnetic shieldingmember stated above as an insert piece. In this case, the rotor magnetis attached to a mounting portion of the rotor magnet of the disk hub40, although not illustrated either, and the magnetic shielding memberis installed in a position which opposes the rotor magnet in the diskhub 40. By this insert molding, the disk hub 40, shaft member 39 andmagnetic shielding member are integrated in a state that the shaftmember 39 passes through the center of the disk hub 40.

As mentioned above, also in the third embodiment, the disk hub 30 ismolded integrally with the shaft member 29 by insert molding, wherebythe process of mounting of the disk hub 30 to the shaft member 29 can bedispensed with and the cost of assembling the motor can be reduced.Furthermore, high mounting precision between the disk hub 30 and shaftmember 29 can be obtained so that sufficient fixing force between themcan be ensured. Moreover, a magnetic shielding member is disposed in aposition in the disk hub 40 which opposes the rotor magnet, wherebymagnetic flux leakage from the rotor magnet can be suppressed.Furthermore, the disk hub 40 can be insert-molded with the core as inthe variation example shown in FIG. 5 also in this embodiment, andaccordingly the molding dimensional accuracy of the disk hub 40 can beincreased.

FIG. 9 is an enlarged sectional view of a polygon scanner motorintegrating a fluid dynamic bearing apparatus 41 according to a fourthembodiment. This embodiment is different from the first to thirdembodiments in that the thrust bearing portion T21 is not a non-contacttype fluid dynamic bearing but a contact type pivot bearing.Specifically, the shaft member 49 has a shaft-like shape without aflange portion, and its lower end 49 b is formed in a convex sphereshape. The shaft member 49 is contactingly supported with its lower end49 b in pivot contact with the inner bottom face 47 c 1 of a thrustwasher 47 c fixed on the housing 47 in the thrust direction.

At this time, for example, the rotor member 50 as a member having apolygon mirror attached thereto and a portion for mounting a rotormagnet is insert-molded by injection molding or like means of a resinmaterial using the shaft member 49 which is previously molded as aninsert piece and, the magnetic shielding member stated above althoughnot illustrated, as an insert piece. In this case, the rotor magnet isattached to the portion for mounting the rotor magnet in the rotormember 50, although not illustrated either, and the magnetic shieldingmember is installed in a position opposing the rotor magnet in the rotormember 50. By this insert molding, the rotor member 50, shaft member 49and magnetic shielding member are integrated in a state that the shaftmember 49 passes through the center of the rotor member 50.

As mentioned above, also in the fourth embodiment, as in the first tothird embodiments, the rotor member 50 is formed integrally with theshaft member 49 by insert molding, whereby the process of mounting therotor member 50 to the shaft member 49 can be dispensed with, and thecost of assembling the motor can be reduced. Moreover, magnetic fluxleakage from the rotor magnet can be suppressed by disposing a magneticshielding member in a position in the rotor member 50 which opposes therotor magnet. Of course in this embodiment, the rotor member 50 can beinsert-molded integrally with the core, and molding dimensional accuracyof the rotor member 50 can be increased as in the above first to thirdembodiments.

The first to fourth embodiments mentioned above describe the case wherea plurality of hydrodynamic grooves 8 a 1, 8 a 2 are provide as ahydrodynamic pressure producing means for producing the hydrodynamiceffect of a fluid in the radial bearing gap of the radial bearingportions R1, R2, but other forms may be also employed. For example,although not illustrated, it is possible to employ a so-called steppedhydrodynamic pressure producing part which has grooves in the axialdirection are formed in a plurality of positions in the circumferentialdirection or a so-called multilobe bearing in which a plurality ofarcuate faces are arranged in the circumferential direction and aradial-direction gap (bearing gap) having a wedge shape is formedbetween these faces and the opposing outer circumferential surface 9 aof the shaft member 9.

Moreover, one or both of the thrust bearing portions T1, T2 (T11, T12)may be constituted of a so-called step bearing in which a plurality ofhydrodynamic grooves in a radial groove shape are provided in a regionwhich serves as a thrust bearing face, at predetermined intervals in thecircumferential direction, or a wave bearing (having a wave shapeinstead of the steps) or like bearings, although not illustrated either.

Moreover, the above embodiments describe the cases where the radialbearing face is formed on the side of the bearing sleeve 8, while thehydrodynamic pressure producing part is formed on the side of thehousing 7, 37. However, the face where these hydrodynamic pressureproducing parts are formed is not limited to those of the parts on thefixed side, and can be, for example, the side of the shaft member 9 andflange portion 9 b, 39 b opposing these parts, or on the side of thedisk hub 10, 13, 30 (rotation side).

INDUSTRIAL APPLICABILITY

This fluid dynamic bearing apparatus is suitable for spindle motors forinformation appliances, for example, HDD and like magnetic diskapparatuses, CD-ROM, CD-R/RW, DVD-ROM/RAM and like optical diskapparatuses, MD, MO and like magneto-optic disk apparatuses, polygonscanner motors of laser beam printers (LBP) or small motors for axialfans and the like.

1. A fluid dynamic bearing apparatus comprising: a shaft member; afixed-side member which freely rotatably supports the shaft member; amember which is attached to the shaft member and has a portion formounting a rotor magnet; and a magnetic shielding member, wherein theshaft member is supported in a radial direction in a non-contact mannerby a hydrodynamic effect of a fluid which is produced in an annularradial bearing gap between the fixed-side member and the shaft member,wherein the member having the portion for mounting the rotor magnet isformed of a resin, wherein the magnetic shielding member comprises amagnetic substance and has an approximate L-shape in cross section, themagnetic shielding member including an axial direction portion extendingin an axial direction and a radial direction portion extending in theradial direction from an end portion of the axial direction portion, theaxial direction portion and the radial direction portion being formedintegrally with each other, the magnetic shielding member being disposedin the member having the portion for mounting the rotor magnet, andwherein the rotor magnet is fixed to an outer periphery of the axialdirection portion of the magnetic shielding member so as to oppose theradial direction portion of the magnetic shielding member.
 2. A fluiddynamic bearing apparatus according to claim 1, wherein the memberhaving the portion for mounting the rotor magnet is an injection-moldedarticle of a resin using the magnetic shielding member as an insertpiece.
 3. A fluid dynamic bearing apparatus according to claim 1,wherein at least part of the magnetic shielding member is embedded inthe resin.
 4. A fluid dynamic bearing apparatus according to claim 1,wherein the magnetic shielding member is formed by plastic processing.5. A fluid dynamic bearing apparatus according to claim 1, wherein themember having the portion for mounting the rotor magnet is aninjection-molded article of a resin using the magnetic shielding memberand the shaft member as insert pieces.
 6. A fluid dynamic bearingapparatus according to claim 1, wherein the fixed-side member comprisesa bearing sleeve into which the shaft member can be inserted at an innerperiphery of the bearing sleeve, and a housing having the bearing sleevefixed thereinside, the housing having an opening portion on one end sidethereof and an integral or a separate bottom on the other end sidethereof.
 7. A fluid dynamic bearing apparatus according to claim 6,wherein a thrust bearing gap is provided between the opening portion ofthe housing and the member having the portion for mounting the rotormagnet, and the shaft member is supported in a thrust direction in anon-contact manner by the hydrodynamic effect of a fluid produced in thethrust bearing gap.
 8. A fluid dynamic bearing apparatus according toclaim 6, wherein a thrust bearing gap is provided between a bottom ofthe housing and the shaft member, and the shaft member is supported in athrust direction in a non-contact manner by the hydrodynamic effect of afluid produced in the thrust bearing gap.
 9. A fluid dynamic bearingapparatus according to claim 6, wherein the shaft member is contactinglysupported by the housing.
 10. A motor comprising: a fluid dynamicbearing apparatus according to claim 1; a rotor magnet; and a statorcoil which produces excitation between itself and the rotor magnet. 11.A fluid dynamic bearing apparatus according to claim 1, wherein theradial direction portion of the magnetic shielding member extendsradially outwardly from the end portion of the axial direction portionof the magnetic shielding member.
 12. A fluid dynamic bearing apparatusaccording to claim 1, wherein the rotor magnet is spaced apart from theradial direction portion of the magnetic shielding member in the axialdirection.